The present invention relates to a safety system particularly for a small arms projectile for a small arms weapon.
In our European Patent EP-B-0363079 there is described a small arms projectile for a smooth bore weapon preferably fired from a cartridge with a propellant charge therein, wherein the projectile comprises a generally cylindrical casing, a warhead assembly, said warhead being hollow to accommodate an explosive charge and an initiator therefor, the casing being formed with a firing pin spring biased to a safety position and locked in the safety position by at least one spring biased safety pin, wherein the spring biased safety pin is adapted to release on exit of the projectile from the muzzle of the small arm weapon.
EP-B-0363079 thus describes a projectile having a mechanical safety means for retaining the firing pin in the safety position. The mechanical safety means comprises at least one spring biased safety pin extending normal to the axis of the firing pin and located in a radial bore in the firing pin to prevent axial movement of the firing pin. The safety pin is radially retained by the cartridge.
There is a drawback associated with this arrangement. When the projectile leaves the muzzle of the small arms weapon there is a severe deceleration as it hits still air and this causes the projectile casing to decelerate and a deceleration force to be applied to the firing pin in the direction of the initiator. The shear force applied to the safety pin by the deceleration between the casing and the firing pin prevents ejection of the safety pin until the shear force is overcome by the spring biassing force acting on the pin. The firing pin is thus retained in its safety position by the safety pin. Only when the shear force has reduced will the safety pin release the firing pin. The effect of this is to delay the arming of the projectile by at least 0.1 seconds (or about 10 metres), or more reliably 0.2 to 0.3 seconds, which equates generally to about 20 or 30 metres down range. This means that targets at short range cannot be engaged and even targets of 25 to 30 metres cannot always be engaged reliably.
A further drawback with this arrangement is that there is only one safety means for retaining the firing pin in the safety position. There is a possibility therefore that the explosive charge could be initiated accidentally if the safety pin became dislodged from the firing pin due to the cartridge being damaged, for example.
In order to address these problems EP-B-0363079 suggests the use of a chemical safety means in addition to the mechanical safety means. The chemical safety means includes a layer of combustible adhesive material interposed between the firing pin and an adjacent hollow portion of the casing. The combustible adhesive material is connected to a bore at the rear of the casing adjacent a propellant charge so that it is activated by the explosion of the propellant charge when the projectile is fired.
In this arrangement the combustible adhesive material retains the firing pin in its safe position for a pre-determined period once the projectile has been fired. This prevents any shear forces being generated between the firing pin and the safety pin as the projectile decelerates on hitting still air. In this way ejection of the safety pin occurs immediately the projectile leaves the muzzle of the small arm. The time taken for the combustible adhesive material to release the firing pin and thus arm the projectile is determined by the characteristics of the combustible adhesive material.
A problem with this arrangement is that the combustible adhesive material may deteriorate and become unstable if stored for a prolonged period, particularly if the adhesive is in any way defective. This is a major drawback if a long shelf life is required as is usual for ammunition.
A further problem associated with this arrangement is that manufacturing constraints can result in the combustible adhesive material being insufficiently reliable to ensure that any delay in arming equates to about 3 metres from the user when the projectile is fired.
It is known, e.g. from FR-A-0 424 890, U.S. Pat. Nos. 2,537,855 and 2,564,797, that wholly mechanical contrivances can be used to effect safety latching of firing pins in projectile fuses, and that a firing pins can be used, whilst so latched, to hold an initiator in a safe condition, against forces urging it into an armed condition. None of these prior specifications, however, envisages the provision of increased safety in handling and in use, by means of plural, independently active mechanical safety latches which are designed and configured to be triggered in response to different events in the firing process.
An object of the present invention is to provide a small arms projectile which has a safety means for retaining a firing pin in a safety position prior to firing and releasing the firing pin on application of acceleration forces consequent upon firing.
Another object of the present invention is to provide a small arms projectile which has at least two mechanically independent safety means for retaining a firing pin in a safety position prior to firing.
Another object of the present invention is to provide a small arms projectile which has a safety means for retaining a firing pin in a safety position prior to firing which operates to delay the arming of the projectile on firing in a more reliable manner than hitherto known safety means.
According to an aspect of the present invention there is provided a small arms projectile for a small arms weapon; the projectile comprising:
a generally tubular casing having an axially movable firing pin;
a compression spring providing a resilient force;
a warhead having an explosive charge; and
an initiator having safe and armed conditions and capable, when in its armed condition and when impacted with sufficient force by the firing pin, of detonating the explosive charge of said warhead;
wherein the casing also contains safety release means for releasably restraining the firing pin, against resilient force which tends to move the firing pin away from the initiator, in a safety position whereby said initiator is held by engagement with the firing pin in its safe condition, against an arming force tending to urge the initiator towards the armed condition;
wherein the safety release means comprise first and second mechanical means;
wherein said first mechanical means includes at least one component constructed to be frangible in response to the forces experienced on firing of the projectile, the strength of the frangible element being sufficient to withstand acceleration forces up to 500 g; and
wherein said second mechanical means includes at least one component disposed and configured so as to be ejected from the casing under the influence of said resilient force when the projectile leaves the weapon permitting said resilient force to move said firing pin away from said initiator to an extent allowing said initiator to be urged into its armed condition.
Accordingly, the initiator is movable between an unarmed position and a biased armed position, but is retained in the unarmed position by engagement with the firing pin in the safety position. In this way the initiator can not be armed until the firing pin is moved from the safety position and disengaged from the initiator.
It will be understood that the abbreviation xe2x80x9cgxe2x80x9d used herein represents the acceleration due to gravity. Typically a small arm projectile will experience an acceleration of between 10,000 g and 15,000 g when fired in the chamber of a small arms weapon. The safety release means retains the firing pin in the safety position on application of acceleration forces less than 500 g to prevent accidental arming of the projectile prior to firing. In this way the releasable safety means will protect the user if the projectile is accidentally dropped during handling since the acceleration forces applied to the projectile will generally be less than 500 g.
Moreover the firing pin is caused to be released from said safety position only when the projectile has been fired and only when both the first and second mechanical means have been caused, in a predetermined sequence, to no longer be effective. In this way if one of the mechanical means fails the other will prevent movement of the firing pin from the safety position. Since the safety release means has releasable means which are mechanical, restraint of the firing pin is improved and problems associated with chemical degradation are avoided. Furthermore, this can prevent the firing pin moving towards the initiator when the projectile has been fired and is still in the chamber or bore of the small arm.
Preferably, said firing pin includes a separate axially movable base portion.
Conveniently, said frangible component comprises a shear pin positioned to support said base portion prior to firing of the projectile.
Thus, the first mechanical means is released from the firing pin by initial axial movement of the base portion in a direction away from the initiator. The acceleration forces applied to the base portion on firing can therefore be used to release the firing pin from the first mechanical means.
In another embodiment, said frangible component comprises a discoidal glass element disposed between said base portion and the casing to support said base portion prior to firing of the projectile.
Thus, the first mechanical means is released from the firing pin by initial axial movement of the base portion in a direction away from the initiator. The acceleration forces applied to the base portion on firing can therefore be used to release the firing pin from the first mechanical means.
Accordingly, the frangible component prevents release of the firing pin from the initiator until significant acceleration forces are applied to the base portion when the projectile is fired. The acceleration forces applied to the firing pin, and the base portion, on firing are considerable and in this way the frangible element can be made sufficiently strong to withstand shock loads due to mis-handling prior to firing.
Accordingly, the frangible element prevents release of the firing pin from the initiator until significant acceleration forces are applied to the base portion when the projectile is fired. The acceleration forces applied to the firing pin, and the base portion, on firing are considerable and in this way the frangible element can be made sufficiently strong to withstand shock loads due to mis-handling prior to firing.
Moreover, the frangible element can be readily fabricated and its breaking strength reliably controlled during manufacture.
It is preferred that the initiator is urged to move from its safe condition to its armed condition by rotating about an axis perpendicular to the axis of said casing.
Consequently, the initiator can only rotate to the biased armed position once the firing pin has disengaged.
In another embodiment, the resilient force applied to the firing pin is provided by a compression spring having sufficient stiffness to prevent the firing pin moving into the initiator due to deceleration experienced by the projectile as it leaves the muzzle of a small arm.
Since the firing pin is biased in an axial direction away from the initiator, this can prevent movement of the firing pin towards the initiator immediately the projectile exits the muzzle of the small arm. In this case, the firing pin strikes the initiator only when the projectile impacts the target.
Conveniently, said second mechanical means includes at least one spring biased safety pin.
Thus, the safety pin can be radially restrained in a cartridge from which the projectile is fired. For example, the safety pin is radially restrained by fins which are in turn radially restrained by the internal surface of the bore of the weapon from which it is fired and is released on exit from the muzzle. The projectile is thus armed either immediately on exit or within a short distance after exiting the muzzle of the shotgun.
In preferred embodiments, two spring biased safety pins are provided for release in opposite radial directions. This avoids any imbalance of the projectile once it has been fired.
Preferably, said casing supports a plurality of stabilising fins constrained to lie against the casing prior to firing of the projectile, but capable of deployment when the projectile leaves the weapon; and wherein at least one of said fins prevents ejection of the ejectable component of said second mechanical means until said deployment occurs; the deployment being assisted by motion of said firing pin under said resilient force.
In a particular embodiment, said firing pin is provided with a stabilising disc having a frusto-conical side portion disposed in contact with the ejectable component of said second mechanical means.
Conveniently, said initiator is constructed to generate, when in its armed condition, an initiating explosive charge in response to impact thereon of said firing pin and comprises means for causing said initiating explosive charge to conform to a predetermined shape about an initiator axis and wherein said initiator axis is misaligned with the axis of motion of said firing pin when held in its safe condition.
In a particular case, when the axis of said initiator is misaligned with the axis of motion of said firing pin, shielding means is interposed between the initiating charge and that of said warhead.
In a particular embodiment, said initiating explosive charge is contained in a cup-like structure and said shield comprises a portion of said structure.